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K2 CW and DSP

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John Graf

K2 CW and DSP

I've been experimenting with the DSP filters on my K2 and I have
found several combinations of DSP and crystal filtering that work
very well on CW (at least for me). However, I have run into a
strange phenomenon.

Here is how I reproduce it: I set my crystal filter at its widest
setting (1.8 KHz). The DSP filter is set for "low pass" with noise
reduction on. With this combination, I am able to find two identical
CW signals on either side of a center frequency. It operates just
like a direct-conversion receiver.

So here are a couple of questions for the group: First, has anyone
else seen this happen? If not, do you think it may be a construction
error on the DSP board? How about a screw-up in the filter alignment
or programming?

Thanks and 73,

John, WA6L

--
The world is best viewed through the ears of a horse.

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RobertG

Re: K2 CW and DSP

John...

Perhaps you have your BFO set in the middle of the wide band. That way
you'd get a tone on either side. That said, I sure would like to hear about
the CW filter settings that you found useful.

Thanks in advance.

....robert #5957

At 06/04/2007 12:42, John Graf wrote:

>I've been experimenting with the DSP filters on my K2 and I have
>found several combinations of DSP and crystal filtering that work
>very well on CW (at least for me). However, I have run into a
>strange phenomenon.
>
>Here is how I reproduce it: I set my crystal filter at its widest
>setting (1.8 KHz). The DSP filter is set for "low pass" with noise
>reduction on. With this combination, I am able to find two identical
>CW signals on either side of a center frequency. It operates just
>like a direct-conversion receiver.
>
>So here are a couple of questions for the group: First, has anyone
>else seen this happen? If not, do you think it may be a construction
>error on the DSP board? How about a screw-up in the filter alignment
>or programming?
>
>Thanks and 73,
>
>John, WA6L
>
>
>--
>The world is best viewed through the ears of a horse.
>
>_______________________________________________
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>You must be a subscriber to post to the list.
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Robert G. Strickland PhD ABPH - KE2WY
[hidden email]
Syracuse, New York USA

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Don Wilhelm-3

Re: K2 CW and DSP

In reply to this post by John Graf

John,

That is not a consequence of any construction error, but a consequence
of your filter alignment.

When you align a wide filter for either CW or SSB, do NOT CENTER it.
Use Spectrogram and align it so that the low frequency edge of the
passband cuts off above zero frequency (I prefer 200 Hz at the lowest
corner). In other words, an 1800 Hz wide CW filter should have an audio
response from 200 to 2000 Hz.

Aligned that way, you will not be able to hear a signal go through zero
frequency and come out on the opposite sideband (like a direct
conversion receiver). I would wager that you have that wide filter
aligned so it receives from perhaps 900 Hz down to -900 Hz (the -900 Hz
is on the opposite sideband, so you hear both sidebands for pitches less
than 900 Hz).

If you like a really wide CW filter, try using the OP1 filter instead of
the variable filter (assuming you have the KSB2 installed). It is
flatter and more 'listenable' than using the varaible filter at a wide
setting. I usually recommend setting the variable filter to 1200 Hz wt
the widest although some filters are quite usable out to 1500 or even
1800 Hz, but on some, the passband ripple becomes quiter pronounced at
wider bandwidths.

Spectrogram will show all that to you visually. If you have not used it
to set up your filters, I recommend that you download it (version 5.17
is available free from www.n0ss.net) and try it out.

Once you have the CW filters set the way you want, then you can use the
DSP to augment those filters and improve the ultimate rejection and
provide a sharper filter slope, but operate with the most narrow CW
filter as your first course of action to combat QRM - if you do not,
strong undesired signals in the CW filter passband will capture the
receiver AGC and de-sense the receiver making all signals in the
passband (including the weak one you are trying to copy) weaker -
operating with a narrow CW filter is the only way to combat that (other
than turning off the AGC).

For additional information on filter alignment, check the info on my
website http://w3fpr.qrpradio.com or Tom Hammond's site www.n0ss.net or
on the builder's Resource page of the Elecraft website.

73,
Don W3FPR

John Graf wrote:

>
> I've been experimenting with the DSP filters on my K2 and I have found
> several combinations of DSP and crystal filtering that work very well on
> CW (at least for me). However, I have run into a strange phenomenon.
>
> Here is how I reproduce it: I set my crystal filter at its widest
> setting (1.8 KHz). The DSP filter is set for "low pass" with noise
> reduction on. With this combination, I am able to find two identical CW
> signals on either side of a center frequency. It operates just like a
> direct-conversion receiver.
>
> So here are a couple of questions for the group: First, has anyone else
> seen this happen? If not, do you think it may be a construction error
> on the DSP board? How about a screw-up in the filter alignment or
> programming?
>
> Thanks and 73,
>
> John, WA6L

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John Graf

Re: K2 CW and DSP

In reply to this post by RobertG

Hi, Robert,

Yep -- I am sure that is what it is. You have confirmed what other
people have told me and I will change the BFO this weekend. It is
sure nice to have the resources and experience that I have found on
the Elecraft reflector.

Well, I think filter settings are a lot a chile recipe. Different
people have different ideas of what is good and bad. But having said
that, I am happy to share what works best for me.

I haven't owned the K2 for that long. I also have a K1 and an
IC-746pro. Both of these have different filtering setups, and the
IC-746pro has DSP, but implemented much differently than the K2. So
my settings are the result of experimentation.

I have my 2nd crystal filter set for 800 Hz. I have found that this
is a great compromise between the 1st filter (wide open) and the
narrower filters. This then feeds 800 Hz bandpass to the DSP. So I
just keep the crystal filters at that setting.

The DSP I have set up with 800, 400, and 200 Hz. Noise reduction is
on and set to 2. When I am searching for a signal I keep it at 800.
Once I find the signal I have the option of narrowing the DSP to 400
or 200 if the band is busy.

I have tried both the "soft" and "regular" CW filter settings on
DSP. Honestly, I don't see much difference. However, after
operating on a couple of contests I decided I liked the way things
worked with the regular setting (big 'C' on the filter window) a
little better.

Anyhow, this works for me. Thanks again for your help on the BFO
issue!

73,

John, WA6L

On Jun 5, 2007, at 8:03 PM, Robert G. Strickland wrote:

> John...
>
> Perhaps you have your BFO set in the middle of the wide band. That
> way you'd get a tone on either side. That said, I sure would like
> to hear about the CW filter settings that you found useful.
>
> Thanks in advance.
>
> ....robert #5957
>
> At 06/04/2007 12:42, John Graf wrote:
>

--
The world is best viewed through the ears of a horse.

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John Graf

Re: K2 CW and DSP

In reply to this post by Don Wilhelm-3

Excellent!! Thanks for taking the time to write and for the in-depth
explanation. I am constantly amazed (and grateful) for the expertise
available here on the reflector.

I will be working to correct the problem this weekend. I have used
Spectrogram (though obviously not well) and have a copy. I like your
idea of using the OPT1 filter and will give that a try.

Thanks again and 73,

John, WA6L

On Jun 5, 2007, at 8:54 PM, Don Wilhelm wrote:

> John,
>
> That is not a consequence of any construction error, but a
> consequence of your filter alignment.
>
> When you align a wide filter for either CW or SSB, do NOT CENTER
> it. Use Spectrogram and align it so that the low frequency edge of
> the passband cuts off above zero frequency (I prefer 200 Hz at the
> lowest corner). In other words, an 1800 Hz wide CW filter should
> have an audio response from 200 to 2000 Hz.
>